To prepare stable liquid or gel detergent formulations for automatic dishwashing machines, it is known that phosphate builders which are highly soluble and reversion stable are required. It is further known that the preparation of a homogeneous gel composition which is stable, free-flowing and readily dispensable is achieved by using sodium trimetaphosphate as the builder in combination with potassium hydroxide as an alkaline source. See Rapisarda et al., U.S. Pat. No. 5,213,706. While sodium trimetaphosphate itself is not a sequestering agent, its reaction with the base converts the metaphosphate anion to the tripolyphosphate anion.
Other bases known in the art are not desirable for the present invention because of their reaction with the metaphosphate anion. In particular, if sodium hydroxide is used for the hydrolysis, sodium tripolyphosphate which has a limited solubility, is formed. Hydrolysis with an ammonium hydroxide base will form a soluble tripolyphosphate, but due to the alkanity, ammonia is liberated, therefore, the use of ammonia hydroxide is limited to neutral or acidic formulations, rather than the alkaline compositions of the invention. Also see Rapisarda et al., U.S. Pat. No. 5,213,706.
When sodium trimetaphosphate is hydrolyzed with potassium hydroxide, according to the invention, a soluble sodium potassium tripolyphosphate (SKTP) is formed as follows: EQU (NaPO.sub.3).sub.3 +2 KOH=Na.sub.3 K.sub.2 P.sub.3 O.sub.10 +H.sub.2 O
To prepare such an aqueous detergent composition, it was preferred to slurry the sodium trimetaphosphate with water in a mixing vessel and then add potassium hydroxide in solid or aqueous form. Once the builder and base are slurried into the mixing vessel, the other ingredients, including the premix were added and mixed.
It has been discovered that in compositions containing more than about 23% by weight sodium trimetaphosphate, that the traditional processing procedure results in undesirable viscosities and lumps due to large amounts of suspended solids,
There is therefore a need to provide an improved process for preparing concentrated detergent compositions structured with sodium trimetaphosphate as the builder.